Asus p8z68-v lx problem with sapphire 7970

Hello,

I installed my 7970 on asus p8z68-v lx PCI-E first slot (blue color). I did not get any video signal and usb power to my mouse.
Then I thought it could be the bios problem? I flashed the latest bios, and it still gave me the same issue.

So I sat my 7970 on pci-e second slot (black color). It worked perfectly fine.

I also loaded my bios to default settings, and it could not help. Do I have faulty motherboard? or gpu issue or psu issue?

Before 7970, I used to have 6870 CFX mode. They were pulled without cleaning the gpu driver. They were working fine for many months.

one of my trials happened that I forgot to plug in pci-e 8pin and 6 pin. I noticed there was power for my usb devices but jut no video signal. That was right after I flashed my bios. So, I thought I solved the problem due to my stupidity. I then plugged in back the 8pin and 6 pin. The result still showed the same. no usb power and no video signal.

However, it works flawlessly on the second pci-e slot.

Please help me  

Thanks